ML20151P188
| ML20151P188 | |
| Person / Time | |
|---|---|
| Site: | Catawba  |
| Issue date: | 04/15/1988 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML20151P166 | List: |
| References | |
| NUDOCS 8804260104 | |
| Download: ML20151P188 (22) | |
Text
.-
N o % g e.s %
PLANT SYSTEMS
_3/4.7.8 SNUBBERS LIMITING CONDITION FOR OPERATION 3.7.8 All snubbers shall be OPERA 8LE.
The only snubbers excluded from the l
requirements are those installed on nonsafety-related syst have no adverse effect on any safety-related system.
APPLICA8ILITY: MODES 1, 2,.3, and 4.
MODES 5 and 6 for snubbers located on systems required OPERABLE in those MODES.
ACTION:
With one or more snubbers inoperable, within 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> replace or restore the inoperable snubber (s) to OPERABLE status and perform an engineering evaluatio per Specification 4.7.8q. on the attached component or l
l SURVEILLANCE REQUIREreNTS Etch snubber shall ba demonstrated OPERABLE by performance of the e
following augmented inservice inspectiert program i.n lieu of the requirements j 4'7.8 of Specificatf ort 4.0.5.
5 Inrpection_ Types a.
As used in this specification, type of snubber shall mean snubbers of the same design and manufacturse, irrespective of capacity.
Visual Irspections b.
Snubbers are categorized as inaccessible or accessible during reactor The first inservice visual inspection of each type of snubber shall be performed after 4 months but within 10 months of operation.
commencing POWER OPERATION and shall include all hydraulic and me If less than two snubbers of each type art found in-operable during tne first insarvice visual inspection ical snubbers.
Otherwise, subsequent visual in-the date of the first inspectdon.
spections shall be performed in accordance with the following schedule:
Subsequent Visual No. of Inoperable Snubbers of Each Inspection Period *(
Type Found Ourino Insoection 18 months : 25%
0 12 months t 25%
1 6 months t 25%
2 124 days 25%
3,4 62 days 25%
5,6,7 31 days 2 25%
8 or more "Tne inspection interval for each type of snubber shall not be lengthened fied more than one step at a time unless a generic problem has been identi and corrected; in that event the inspection interval may be lengthened one step the first time and two steps thereafter if no inoperable snubbers that type are found.
- The provisions of Specification 4.0.2 are not analicable.
8804260104 980415 3/4 7-19 fDR ADOCK 05000413 DCD N - UNITS 1 & 2
~ _ _ _ _,
pl. ANT SYSTEMS _
t SURVElluNCE REQUIREMENTS (Continued) iteria c.
Visual Insn::tiv al inspections shall verify that:
(1) there are no visible indi-cations of damage or impaired OPERASILITY,n(2) =ttachments to the foundation or supporting structure are functbnal, ;;d (U feetewee-fec ; = ;h_.;t d Oh; ;;Ct:r t; th: :n:xM~ed t: th: = tt:r
)
Snubbers which ap.: ? inoperable as a x ;h;r:;: n facti;;;.-result of visual inspections may be determined OPERA 8L 5 + % m t " S = ? i,; ;,t;,,, i,,i,,,,el,,,,,; w o
,== af an+ *1 hh4 J
(1) the cause of the rejection is ciearly established and reme-that:
J died for that particular snubber and for other snubbers (regardless of type) that a,ay be generically susceptible; and (2) the affected snubber is functionally tested in the as-found condition and deter-When a fluid port of a hy-mined OPERA 8LE per Specification 4.7.8f.
draulic snubber is found to be uncovered, the snubber shall be declared inoperable and may be deterair.ed OPERA 8LE via functional testing only if the test is started with the piston in the as-found All setting extending the piston rod in the tension mode direction.
snubbers connected to an inoperable common hydraulic fluid reservoir
~
shalT be ceunted as inoperable snutbers.
d.
Refuelino Outace Inspections At each refueling, the systees which have the potential for a severe dynamic event, specifically, the Main Steam System (ups relief valves and piping, Auxiliary Feedwater System, main steam supply to the auxiliary feedwater pump turbine, and the letdown and charging portion of the CVCS System shall be inspected to determine if there In the case of a severe dynamic has been a severe dynamic event.
event, mechanical snubbers in that syStas which experienced the event shall be inspected during the refueling outage to assure that the mechanical snubbers have freedom of movement and are not frozen up.
The inspection shall consist of verifying freedoe-of-mot. i of the following:
uation of in-place snubber piston setting; or (3) stroking the If one or more mechanical snubber througn its full range of travel.
mechanical snubbers are found to be frozen up during this inspection, those snubbers shall be replaced or repeired before returning to power;. The requirements of Specification 4.7.8b. are independent of L
the requirements of this spacification.
e.
Functional Tests e first refueling shutdown and at least once per 18 moR/ar-
. ereaf ter during shutdown, a representative sample of snubbers-e+
Duri n:n ts ; shall be tested using one of the following sample plans.as The large-bore steam generator hydraulic snubbers shall be tr 1
4 3/4 7-20 CATAWBA - UNITS 1 & 2
ptANT SYSTEMS f
SURVEILLANCE REQUIREMENTS (Continued) e.
Functional Tests (Continued) a separate type (population) for functional test purposes.
A 10%
random sample shall be tested at least once per 18 months during refueling with continued testing based on a failure evaluation.
The sample plan shall be selected prior to the test p Aem canna '-
anged during the test period.
The NRC Region Wdministrator shdll be no fied in writing of the sample plan sel cted f:. e::n ;natt:r ty;;
prior to the test period or the sample
_. "cad in the oriam-test period shall be implemented:
1)
At least 10% of all snubbers shall be fu onally te:t-ither in place or in a bench test.
For each nubber-:f : ;;;; that does not meet the functional test acc tance cr'?eria of Sp cification 4.7.8f., an additional 10% o
_11 snubbar be -
functionally tested until no more failures are found or until all snubbers have been functionally tested; or 2)
A representatiW< m e c.r a s i wsu :"11 be functionally <
tested cordance with Figure 4.7-1.
"C" is the umber of unbers :f : ty;; found not meeting the acceptance requi ents of Specification 4.7.8f.
The cumulative number of snub-bars tested is denoted by "N".
At the end of esch day's test-(
ing, the new values of "M" and "C" (previous day's total plus current day's increments) shall be plotted on Figure 4.7-1.
!?
- n3 ti;; th ;; int ;!
- tt:0 f:11: in :n; "":j;;;" r;;i:n, :11
- nutt:r:
' th:t ty;; :h:11 5: functi:n:1?y t::t:0, If at any time the point plotted falls in the "Accept" region, testing of l
snubbers':f th:t ty;; may be terminated.
When the point plotted lies in the "Continue Testing" region, additional snubbers e*
th:t 03;; shall be tested until the point falls in the "Accept" racion er th: "": M r:;i:n, or all the snubbers f th:t 03p:
have been teste 4
An ir
'ai representative samole of 55 snuobers shall be fun onu ly tested.
For each snuceer type which does not m the etional test acceptance criteria, another sa of at least on if the size of the initial sample s be tested until the tot umeer tested is equal to t initial sample sJze multiplied by factor, 1 + C/2 are "C" is the number of snubbers found which not mee e functional test accept-ance criteria.
The results his sample plan shall be plotted using an "Accept"
~
follows the equation ew N = 55(1 + C/2).
Each ubcer point Id be plotted as soon as the snuab s tested.
If the poi lotted falls on or below the "Ac
" line, testing may be termina If the point plo d falls above the "Accept" line, testin st continue until e point f alls in the "Accept" region or all the oers hat type have been tested.
CATAWBA - UNITS 1 & 2 3/4 7-21
PLANT SYSTEMS SURVEILLANCE REQUIREMENTS (Continued) e.
Functional Tests (Continued)
Testing equipment failure during functional testing may invalidate that day's testing and allow that day's testing to resume anew at a later time provided all snubbers tested with the failed equipment during the day of equipment failure are retestad.
The representative sample selected for the functional test sample plans shall be random-ly selected from all snubbers and reviewed before beginning the test-ing.
The review shall ensure, as far as practicable, that they are representative of the various configurations, operating environments, range of size, and capacity of snubbers.
Snubbers placed in the same location as snubbers which failed the previous functional test snall be retested at the time of the next functional test but shall not be includad in the sample plan.
If during the functional testing, addi-tional sampling is required due toJailur; cf nir On: tycc Of Crut
% the functional test results shall be reviewed at that time to spec de g rm pej, a g gna {saggigs g g,be] p ed to 0,e M e M pye
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Oc5e SnbG h f.
Functional Test Acceotance Criteria r
hV hkre <noAc.deddied 4gne The snubber functional test shall verify that:
Lediond 4 in3 1)
Activation (restraining action) is achieved within the specified range in both tension and compression, except that inertia de-pendent, acceleration limiting mechanical snubbers may be tested to verify only that activation takes place in both directions of travel; 2)
Snubber bleed, or release rate where required, is present in both tension and compression, within the specified range; 3)
For mechanical snubbers, the force required to initiate or maintain motion of the snubber is within the specified range in both directions of travel; and 4)
For snubbers specifically required not to displace under continuon load, the ability of the snubber to witnstand load without displacement.
Testing methods may be used to measure parameters indirectly or parameters other than those specified if those results can be correlated to the specified parameters through established metneds, g.
Functional Test Failure Analysis An engineering evaluation shall be made of each failure to meet tne L 56*.T functional test acceptance criteria to determine the cause of tne FRos failure.
The results of this evaluation shall be used, if applicable, in selecting snubbers to be tested in an effort to determine the ggyy OPERABILITY of other snubbers-irrespecti e cf typc which may be PA4E subject to the same failure mode.
CATAWBA - UNITS 1 & 2 3/4 7-22
INSERT FOR PAGE 3/4 7-22 An independent test failure mode group consisting of all unacceptable snubbers that have a given failure mode, and all other snubbers subject to the same failure modo, shall be separated for continued testing apart from the general population of snubbers. A supplemental test lot of snubbers for each independent test failure modo group shall be tested from the defined testing plan group.
This supplemental test lot will be calculated based on each independent test failure mode group representing C=1 from Figure 4.7-1 or 10% of the remaining snubbers in the test plan group for the 10% testing plan. Failures in the supplemental lot require additional testing in the defined test plan group unless an engineering evaluation indicates another group is appropriate.
The number of unacceptable snubbers which define the test failure mode group shall determine the additional testing in the test failure modo group as follows:
(1) Snubbers are selected in a random manner from the independent test failure mode group.
(2) Any additional unacceptable snubbers found in the independent test failure modo group shall be counted for continued testing only for the independent test failure modo group.
(3) Testing will be complete for each independent test failure mode group when:
(1) 10% Plan 10% tested from the failure mode group for each unacceptable snubber in the failure mode group has satisfied the acceptance requirement in 4.7.8f., or (2) 37 Plan Figure 4.7-1 is satisfied meeting the acceptance requirement in 4.7.8f. using the following guidelines:
For independent test failure mode group:
N = Initial defined test plan lot of 37 tested plus all those selected and tested from the independent test failure mode group.
C = Total number of unacceptable snubbers in the independent test failure mode group.
I~O T~h'tr fA56 NO CNM4GS ad' l
PLANT SYSTEMS
(
l SURVEILLANCE REQUIREMENTS (Continued)
Functional Test Failure Analysis _ (Continued) g.
For the snubbers found inoperable, an engineering evaluation shall be performed on the components to which the inoperable snubbers are The purpose of this engineering evaluation shall be to attached.
determine if the components to which the inoperaole snubbers are attached were adversely affected by the inoperability of the snubbers in order to ensure that the component remains capable of meeting the designed service.
l If any snubber selected for functional testing either fails to lock up or fails to move, f.e., frozen-in-place, the cause will be evaluated and, if caused by manufacturer or design deficiency, all snubbers of the same type subject to the same defect shall be func-This testing requirement shall be independent of tionally tested.
the requirements stated in Specification 4.7.8e. for snubbers not l
meeting the functional tast acceptance criteria, 7
Functional Testino of Repaired and Roolaced Snubbers..
.t b.
Snubbers which fail the visual inspection or the functional test Replacement acceptance criteria'shall be repaired or replaced.
snubbers and snubbers which have repairs which might affect the functional test result: 'shall be tested to meet the functional test-criteria before installation in the unit.
Mechanical snubbers shall have met the acceptance criteria subsequent to their most recent service, and the freedom-of-motion test must have been performed within 12 months before being installed in the unit.
i.
Snubber Service Life Procram If a The service performarce of all snubbers shall be monitored.
service lifetime limit is associated (established) with any snubber (or critical part) based on manufacturer's information, qualification tests, or historical service results, then the service life shall be monitored to ensure that the service life is not excee surveillance inspections.
extended or shortened based on monitored test results and failure The replacements (snubbers or critical parts) shall be cocu-mentet and the documantation shall be retained in accordance history.
Specification 6.10.2.
3/4 7-23 CATAWBA - UNITS 1 & 2
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8 n
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7 49, E999P, 3
s 6
4, v
C 5
i s
4 o p; CONTINUE TESTING 7
m 3
gp.k 2 r h,
ACCEPT l
1 e
i 0
10 20 30 40 50 60 70 80 90 100 N
FIGURE 4.7-1 SAMPLE PLAN 2) FOR SNUBBER FUNCTIONAL TEST 3/4 7-24 CATAWBA - UNITS 1 AND 2
)
PLANT SYSTEMS l
BASES SNUB 8ERS (Continued)
The~ visual inspsetion frequency is based upon mE3ntaining..a constant level
~
of snubber. protectionr during an earthquake or-severe transient..Therefore,.the -
required ' inspect' ion interval /v'ariet einv'ersely with the observed.snubtier.f ailures and is determined by the number of inoperable snubbers found during an inspec-tion.
In order to establish the inspection frequency for each type of snubber, it was assumed that the frequency of snubber failures and initiating events are constant with time and that the failure of any snubber on that system could cause the systes,to be unprotected and to result in failure during an assumed I ni ti at.i ng ' event.
Inspections performed before that interval has elao. sed may be used as a new reference point to determine the next inspection.
However; the results of such early inspections performed before the original required time interval has elapsed (nominal time less 25*.) may not be used to lengtnen the required inspection interval.
Any inspection whose results require a shorter inspection intervt.1 will override tne previous schedule.
The acceptance criteria are to be used ia the visual inspection to determine OPERASILITY of the snubbers.
To provide as'surance of snubber functional reliability, die of 9 3
functional testing methods are used with the stated acceptancip ertar 1.
Functionally test 10% of a type of snubber with an additional 10% tested for each functional testing failure, or
.7 x
se Functionally test, a sample size and determine sample ace
.;j u ti;n using Figure 4.7-1, as.
2.
"; nth =il;, tu t :.;;c;nn u ti a n.r i; ;i;; and C u mi ; x:;l; u n ;;= = ;r 7;j nti;r. i.; =.n n: G = ti;r Figure 4.7-1 was developed using "yld's Sequential Procaciiicy natio Plan" as described in "Quality Control and Industrial Statistics" by Acheson J.
Duncan.
Permanent or other exemptions from the surveillance program for individual snubbers may be granted by the Commission if a justifiable basis for exemption is presented at4, if applicable, snubber life testing was performed to qualify Snubbers so exempted shall the snubber for the applicable design conditions.
be listed in the list of individual snubbers indicating the extent of the i
exemptions.
j CATAWBA - UNITS 1 & 2 8 3/4 7-5
e 9
0 0
ATTAGDIENT 2 DISCUSSION AND ANALYSIS OF NO SIGNIFICANT HAZARD CONSIDERATIONS 1
sv 4
CHANGE 1 - DELETION OF SURVEILLANCE 4.7.8e.3)
Surveillance Requirement 4.7.8e.3) presents one of three options to be selected for use as a snubber sample plan.
This particular test plan has never and will never be used at Catawba. The other two plans under functional testing; the 10% plan (e.1) and the 37 plan (e.2),
l will be sufficient for any testing at Catawba. Likewise in the most recent draft of 0M-4, Revision 2 (draft 6), the 55 sample plan has been deleted. OM-4 is an Operating and Maintenance working group which develops and writes codes for ASME,
The working group is comprised of technical experts from utilities, vendors, and regulatory agencies..
10 CFR 50.92 states that a proposed amendment involves no significant hazards considerations if operation in accordance with the proposed amendment would nots (1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of
. accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin of safety.
(1) The proposed amendment does not involve an increase 2n the probability or consequences of any previously evaluated accident. The probability and/or consequences of an accident previously evaluated remain unchanged. Deletion of the 55 functional test sample plan (Surveillance 4.7.8e.3) will not have a significant effcet on the design or operation of the station since this 1
plan has never been implemented, t
(2) The proposed change will not create the possibility of a new or different kind of accident from any accident previously evaluated because the amendment will not result in a change to the design or operation of the station.
All snubbers will still be required to be operable and appropriate snubber inspections will continue to be performed. The 55 plan has never been used, as such, this change will not create the possibility of a new or different kind of accident from any accident previously evaluated.
(3) The proposed change will not result in a significant reduction in a margin of safety.
Removing surveillance 4.7.8e.3) will result in the deletion of one of three sample options. As such, the requirements of the specifications will be more restrictive.
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CHANGE 2 - DELETION OF THE ' REJECT' LINE This change would allow deletion of the reject line from Figure 4.7-1 and in the 37 functional test sample plan (Surveillance 4.7.8e.1).
The justification for this has already been evaluated for the McGuire Technical Specification change issued September 30, 1985.
This change has also been agreed upon by the OH-4 working group for Revision 2 of the OM-4-standard.
Deletion of the "REJECT" line will remove the possibility of rejecting a good population of snubbers which would require unnecessary testing of the total population of approximately 1600 snubbers.
The discussion of'the statistical significance of deleting the reject line was presented as justification for the McGuire amendment. This discussion is applicable to Catawba and is presented here as Attachment 3.
10 CFR 50.92 states that a proposed amendment involves no significant hazards considerations if operation in accordance with the proposed amendment would'not:
(1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve'a significant reduction in a margin of safety.
(1) Deletion of the "REJECT" line will not involve a significant increase in the probability or consequences of an accident. Deletion of the "REJECT" line will omit the possibility of rejecting a good population of snubbers without increasing the possibility of passing a bad population.
The requirement to continue testing additional samples of snubbers if inoperable snubbers are found will remain in the specifications.
(2) The proposed change will not create the possibility of a new or different kind of accident from any accident previously evaluated because the amendment will not result in a change to the design or operation of the station.
All snubbers will still be required to be operable and appropriate snubber inspections will continue to be performed. As such, this change will not create the possibility of a new or different kind of accident from any accident previously evaluated.
(3) The proposed change will not tesult in a significant reduction in a margin of safety.
Deletion of the "REJECT" line will remove the possibility of unnecessarily having to test all of the snubbers at the station. The requirement to test additional samples of snubbers when inoperable snubbers are found will be retained. Therefore this change will not significantly reduce a margin of safety.
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CHANGE 3 - CLARIFICATION OF FAILURE MODE GROUPING The present Catawba Technical Specification addresses failure mode grouping in paragraph g. under functional tsst failure analysis, but does not give any specific direction of how to implement this.
Discussions were held on November 10, 1987 with Mr. Horace K. Snaw of the NRC Staff to address this issue.
The agreed upon direction for implementing failure modo grouping is what is being proposed at this time in Specification 4.7.8g.
This proposal also agrees with OM-4, revision 1 and the most recent draft of OH-4, revision 2 (draft 6).
10 CFR 50.92 states that a proposed amendment involves no significant hazards considerations if operation in accordance with the proposed amendment would not:
(1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin or safety.
(1) Addition of the words describing failure mode grouping is intended to clarify the current practice and therefore will not involve a significant increase in the probability or consequences of any previously evaluated accidents.
(2) The proposed change will not create the possibility of a new or different kind of accident from any accident previously evaluated because the amendment will not result in a change to the design or operation of the station.
All snubbers will.still be required to be operable and appropriate snubber inspections will continue to be performed. As such, this change will not create the possibility of a new or different kind of accident from any accident previously evaluated.
(3) The wording changes to surveillance 4.7.8g. are intended to clarify existing practice. Therefore, these changes will not effect any margin of safety.
CHANGE 4 - DELETION OF '0F A TYPE' FROM SURVEILLANCE 4.7.8e This proposed change would allow deletion of the phrase "of a type" in paragraph 4.7.Be.
The use of this phrase penalizes Catawba Nuclear Station when/if they upgrade to a better snubber.
It requires a new sample plan be initiated for every type snubber. Our 95/90 confidence level is maintained with one or more than one type of snubber, since each type snubber is represented in the 37 test plan in a percentage relative to that in the field.
If during functional testing a snubber is identified as unacceptable, a failure mode group (based on type, location, etc...) is separated from the general population and additional testing is performed in both groups to assure a good population.
Failure mode gtouping is the method used in OM-4 and at McGuire to assure homogeneity of the general population and address the issue of type. Homogeneity is assured on the basis of visual examinations and functional testing, not on the basis of size or type.
10 CFR 50.92 states that a proposed amendment involves no significant hazards considerations if operation in accordance with the proposed amendment would nots (1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from wiy accident previously evaluated; or (3) Involve a significant reduction in a margin of safety.
(1) Deletion of the phrase "of a type" will remove unnecessary restrictions from the snubber specification. The requirement to have all snubbers operable will not be affected by this change, therefore there will be no change to the results of any previously evaluated accidents.
(2) The proposed change will not create the possibility of a new or different kind of accident from any accident previously evaluated because the amendment will not result in a change to the design or operation of the station.
All snubbers will still be required to be operable and appropriate snubber inspections will continue to be performed. As such, this change will not create the possibility of a new or different kind of accident from any accident previously evaluated.
(3) The proposed change will not result in a significant reduction in a margin of safety.
The entire population of snubbers will be adequately maintained independent of how mar.y different "types" may exist. Adequate testing and inspection will still be required to ensure that the snubbers will remain operable.
)
CHANGE 5 - DELETION OF REQUIREMENT TO INSPECT ATTACHMENT HARDWARE Surveillance '4.7.Pc, Visual Inspection Acceptance Criteria goes beyond inspection of the snubber and its attachment to supporting structures.
It also requires inspection of the attachment hardware. This inspection is already under the requirements of ASME Sect XI IWF, which the OM-4 working group has acknowledged.
The inspection plan (ISI) required by the ASME Code,Section XI, IWF for hanger supports, including snubbers, is performed under procedure using a certified VT-3 inspector.
For the snubber Technical Specification to require more stringent visual inspections for snubbers (which are needed to function during an earthquake) than on other piping supports (which are always needed to function) is an undue burden on the plant staff.
Approximately 1000 snubbers require removal and replacement of mirror insulation in order to perform this inspection. Because of the potential for the creation of airborne indioactivity as a result of removing the insulation, respirator protection is required for any jobs being performed in the area.
It is estimated that the cost associated with this work is in excess of $100,000 each year. This change is recommended so that unnecessary man-rem and man-hours can be saved.
10 CFR 50.92 states that a proposed amendment involves no significant hazards considerations if operation in accordance with the proposed amendment would not:
(1) Involve a significant increase in the probability or consequences of an accident previously evaluated; or (2) Create the possibility of a new or different kind of accident from any accident previously evaluated; or (3) Involve a significant reduction in a margin of safety.
(1) Deletion of the requirement to inspect attachment hardware will remove an unnecessary burden from the snubber specification. This inspection is l
already required under Section XI of the ASME Code. The Section XI t
inspection will be performed as required, thus this change will not significantly inctease the probability or consequences of any previously evaluated accident.
(2) The proposed change will not create the possibility of a new or different kind of accident from any accident previously evaluated because the amendment will not result in a change to the design or operation of the station.
j All snubbers will still be required to be operable and appropriate snubber l
inspections will continue to be performed. As such, this change will not create the possibility of a new or different kind of accident from any accident previously evaluated.
l (3) Deletion of the requirement to inspect the snubber attachment hardware will eliminate an unnecessary amount of inspection. Since this inspection is required to be performed per Section XI of the ASME Code, deletion from the j
specifications will not result in a significant reduction in a margin of i
safety.
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ATTACHMENT 3 STATISTICAL ANALYSIS FOR DELETI;N OF REJECT LINE
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.,8 DUKE POWER COMPANY
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GENEIt AL OFFICES
" ff.'M era sourn cuview stagit CIrAltLo rrc. N. C. 2S242 February 27, 1985 Re: 0&M-4 Task Force Functional Test Sampling Plan As agreed upon at our 2/15/85 meeting in Bethesda, we have performed some parameter studies using the Wald sequential sampling plan equations from page 345 -
of "Applied Statistics for Engineers", and using the OCM-4 37 plan as a base.
Results follow:
8 Series I (See Attached Sheet Labled "Series I")
- 3 = Quality (% Bad) of a good population =.025 e = Probability of rejecting a good population Variable =.10 thru zero P = Quality (% !ad) of a bad population =.10 2
g = Probability of accepting a bad population =.05 Series 11 P = Variable =.01 thru.05 i
g o< =. 0 5 P =.10 2
g =.05 Series ill P =.025 3
- < =.05 P7=
Variable =.10.
11 g =.05 The results of Series I seem nest interesting.
Changing H' the probability of rejecting a good population had no significant irrpact on the accept line. The s lo::es were identical, and for cK varying from.10 to.001, the lower intercept (H ) changed only from 197 to 2.04 On the other hand, the str. aller we made o<, the higher the g
rej ect line went. When we set o< =
0, the reject line disappeared completely ( h -cc).
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Inspection of the equations shows why this occurs, ex S d are not in the slope equation, and w is a very weak pararacter in the /y equation.
A_ major change in the reject line caused only a tiny change in the accept line, while continuing to accept a marginal population (10% Bad) only 5% of the cree, in a practical sense, that proves that acceptance is independent of rejection.
we plot impacts only on rejection, acceptance is independent of when we plot.
Since when We have been thinking that th2re must be an impact of non-rejection on acceptance in that some campaigns with bad populations that would have rejected on a plot-by snubber basis, but would not reject on a plot-by-lot basis.
Subsequently, the cam:aigt could accept and thereby logic is sound, but we may be misjudging the magnitude of the ef fect. in The Figure 1, we can see that only two points (n = 37, C = 364) need be considered.
Referring to (C < 3 always accepts, C > 4 always rejects, regardless of which method of plo is used).
With a 10% bad population, the probability of arriving at (n = 37, C = 3), rejec on the way, is only about 2%.
is about 2%, so the total probability of false acceptance byFrom that point on, this route is ( 02)2.,og which is negligible.
The probability of arriving at is about 20%, and the probability of a false acceptance from there is less that(37 Also negligible.
23.
These two points are too close to the reject line, and too far frc-the accept line to have mucn chance of accepting.
(I hope you will check those calculations independently).
This indicates that the probability of false acceptance of a bad population is real but negligible, which is consistent with the results of the Series 1 studies on the Wald.
It is also consistent with what David Rubenstein told us on 2/15/85 he told us on 1/8/81.
, anc wnat (Vith David Rubenstein's copy of this letter, I am including a copy of Ralph Birkel's 1/15/81 summary of that meeting to help David that event).
reconstruct Se r l et-II, Vald curves show a dependence of the accept line on P), the estimated quality of a good population.
and intercepts offsetting in the region of interest.The curves are bunched up to P; M
.03, with slope At P;
o Uset e Uect begins to dominate, and at P; =.05 the ef fect is clear.
We should confirm our judgement that P should be in the 2.5% range.
I believe the confirmation is in the curves plotted o;n Figure 2.
The amount of testing required and the risk of rejection are clearly unacceptable at 4t, bad (37 Plan), and, at 2 + 0 with the 55 plan.
(We'll have more confidence in our calculation of the risk of rejection by the 3/7/85 meeting.)
If I were free to do it over, I believe I would pick P between 2% and 2 R,C<
=
.01.
g
-._.__..__m i.
Q-i That's probably more'than you can stand for now.
See you March 7.
- i Very truly yours, T. F. Wyke, Chief Engineer Mechanical and Nuclear Division i
k I
3 4 er i
By:
D. M. Colli s, Senior ngineer DMC: emf I
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